Antihistamines in GI
First-generation antihistamines (also called sedating antihistamines) are used to treat motion sickness and nausea during pregnancy. Their exact mechanism of action for nausea is not well understood. It is presumed that antihistamines act in the pathway from the vestibular centre towards the CTZ on the H1 receptor. However, the sedativeeffect also probably plays a major role in the anti-emetic effect.
Finally, the first-generation antihistamines are also highly anticholinergic, thus decreasing muscle contraction and motility of the GI-tract.
Meclozine is a member of the first generation antihistamines used for nausea, vomiting, and motion sickness. As result of its mechanism of action, drowsiness and sedation are the most common side effects.